It is known in the art that fluorocarbon solvents, such as trichloromonofluoromethane, exhibit good stability when compared with chlorinated solvents such as methylchloroform, trichloroethylene, perchloroethylene or methylene chloride. In addition the fluorocarbon solvents are less toxic and are not classified as hazardous materials whereas the chlorinated solvents are considered hazardous, and contain inhibitors which may or may not evaporate faster than the solvent but are required to prevent the formation of toxic decomposition products.
It is known that fluorinated solvents perform well in cleaning and degreasing applications and these applications are even further broadened when the fluorocarbon solvent is mixed with a polar solvent such as an alcohol. Such mixtures exhibit greater solvency power, greater wettability of hydrophilic surfaces, better penetration into hydrophilic substrates and improved heat dissipation due to low surface tension and improved thermal conductivity. Although these advantages can be achieved by mixing fluorocarbon solvents with alcohols in any ratio, it would be preferable to have a mixture of the fluorocarbon solvents and alcohol which boils at a constant temperature in which the amount of alcohol is at a minimum in order to maintain the basic characteristics of the fluorocarbon, eliminate fire hazards due to the presence of the alcohol and to permit purification of the fluorocarbon alcohol mixture by distillation without fractionation. Unfortunately the existence of such constant boiling mixtures cannot be predicted.
Prior art azeotropic mixtures of fluorocarbon solvents with alcohols had an alcohol content, which increased the likelihood of flammability or at least had sufficient alcohol to adversely affect the basic characteristics of the fluorocarbon, e.g., to cause corrosion of a metallic substrate.
An example of such a prior art constant boiling mixture is disclosed in U.S. Pat. No. 3,477,952 which is a composition which boils at a substantially constant temperature consisting of 98 to 96.5 percent by weight trichlorofluoromethane and 2 percent to 3.5 percent by weight methanol. This prior art constant boiling mixture requires too much methanol in that the basic characteristics of the fluorocarbon are affected. For example the use of the trichlorofluoromethane-methanol constant boiling mixture to remove soldering fluxes from circuit boards is not satisfactory in that the high percentage of methanol will attack and dissolve photoresists on the surface of the circuit board. In addition the presence of methanol in a constant boiling mixture or any other mixture creates a toxicity hazard. Furthermore the presence of methanol in conjunction with a fluorinated hydrocarbon such as trichlorofluoromethane results in a composition which will react with certan metallic substrates, e.g. titanium.
A constant boiling composition between a fluorocarbon and alcohol is therefore desirable which contains less than 2 percent alcohol and which contains no methanol.